Technical Field
Exemplary aspects of the present invention relate to a fixing device and an image forming apparatus incorporating the fixing device.
Related Art
Contemporary image forming apparatuses such as copiers, printers, facsimile machines, or multifunction peripherals having two or more copying, printing, and facsimile functions are expected to improve energy saving efficiency, accelerate operation speed, and enhance image quality. However, thermal efficiency of a fixing device used in the image forming apparatus needs to be improved, and heat of various rollers in the fixing device needs to be controlled with precision to meet such recent market demands.
The image forming apparatus, which employs an image transfer method or a direct method, performs an image forming process to form an unfixed toner image on a recording medium (also referred to as a recording material or paper) such as a recording material sheet, printing paper, photosensitized paper, or electrostatic recording paper. The image forming process includes electrophotographic recording, electrostatic recording, and magnetic recording. A fixing device that employs a contact heating method is widely used to fix the unfixed toner image on the recording medium. The contact heating method includes a heating roller method, a belt fixing method, a film heating method, and an electromagnetic induction method.
Herein, the fixing device employing the heating roller method includes a fixing roller and a pressing roller as a rotation roller pair as a basic configuration. The fixing roller includes a heat source such as a halogen lamp, the temperature of which is adjusted to a predetermined temperature. The pressing roller is pressed by the fixing roller. A recording medium is conveyed to a contact portion called a fixing nip (also referred to as a nip portion) between the rotation roller pair, so that an unfixed toner image is fixed with heat and pressure applied by the fixing roller and the pressing roller.
On the other hand, the fixing device employing the belt fixing method includes a fixing roller disposed opposite a pressing roller, and an endless fixing belt (a fixing rotator) looped around the fixing roller and a heating roller. In a fixing nip formed by contacting the pressing roller and the fixing belt, heat from the heating roller is applied to a recording medium via the fixing belt, and an unfixed toner image is pressed to the recording medium to fix the unfixed toner image on the recording medium.